The invention relates generally to the coking of coal.
The coking of dry coal, that is, coal which has been preheated to temperatures of 150.degree. to 250.degree. C, for example, provides the advantage that savings in the heating costs associated with the production of coke may be realized. Thus, whereas the heating required for the coking operation is costly, it is possible to preheat the coal using relatively inexpensive heating means. Furthermore, the preheating of the coal permits coke of higher quality to be produced therefrom and, in particular, permits coke of larger particle size and greater abrasion resistance to be obtained than would be possible otherwise. As a result of this, it is possible to produce a relatively good quality of coke from coal having relatively poor coking characteristics by preheating the coal.
It is already known to pneumatically convey preheated coal from a supply container into the individual chambers of a coke oven battery via a branched conduit system. With this filling technique, ignitions and explosions occur in the oven chambers. The explanation for this resides in that the coal must be admitted into the oven chambers with a considerable amount of force, and accordingly, the blowing of the coal causes the hot coking coal to be admitted into the individual chambers in the form of streams so that part of the coal comes into contact with the hot atmospheres in the chambers, as well as with the hot chamber walls, in the form of a fine dust cloud. The above filling technique requires a strong blowing of the coking coal into the chambers in order to achieve a uniform filling of the coal over the entire lengths of the respective chambers. It is apparent that the filling technique just described has associated with it the disadvantage that there exists a particularly strong propensity for the development of dust and, concomitantly, an increased danger of explosion.
It has been proposed, in order to suppress the danger of ignition and explosion, to add between 0.5 and 5 percent by weight of residual oil, or residual oil in admixture with pitch, to the preheated coal. This proposal was intended to make it possible to pneumatically admit the hot coal into the coke oven chambers without danger. Evidently, this proposal contemplates for the fine dust particles to be agglomerated by means of the residual oil so that these dust particles become harmless as a cause of dust explosions. The reason for the selection of residual oil, in admixture with pitch if desired, from among the many known oils which are effective for binding dust is based on the fear that the addition of oils of lower boiling point to the coal might create an additional fire and explosion hazard rather than suppressing such hazard. With residual oil, in admixture with pitch if desired, such danger should be small since residual oil contains only small amounts of readily volatilizable constituents.
The addition to the coal of residual oil, in admixture with pitch if desired, does not, however, prevent substantial amounts of coal dust from being carried out of the oven chambers into the collecting means exteriorly thereof. Thus, as a rule, an additional formation of dust takes place in the upper regions of the oven chambers towards the end of the filling operation. The reason for this resides in that the gases which develop as a result of degasification rise through the coal charge in the chambers and, for a certain period of time, cause the coal to be in a fluidized state in the upper regions of the chambers. With the above-described method, the quantity of coal dust carried out of the chambers is between approximately 30 and 50 kilograms per ton of coal.
The coal dust which escapes from the oven chambers and enters the collecting means is referred to as "carry over" in the art. This coal dust forms a highly viscous mass in the collecting means which is difficult to remove. Moreover, a portion of the dust is carried into the tar separator by the condensate flowing out of the collecting means. In the tar separator, the dust leads to the formation of an emulsion during the separation of the tar and the water and, as a result, gives rise to difficulties in the tar separator.